Palm Unit for Artificial Hand

ABSTRACT

A palm unit for an artificial hand comprises: a palm unit body ( 70 ); a motor ( 68 ) held by the palm unit body ( 70 ); a hydraulic pump assembly ( 72 ) held by the palm unit body ( 70 ) and comprising a low-pressure hydraulic pump ( 76 ) and a high-pressure hydraulic pump ( 74 ), wherein both hydraulic pumps ( 74, 76 ) are powered simultaneously by the motor ( 68 ); and a hydraulic circuit held by the palm unit body ( 70 ) and coupled to both hydraulic pumps ( 74, 76 ), wherein the hydraulic circuit has a low-pressure configuration in which the discharge sides of both hydraulic pumps ( 74, 76 ) a re coupled to one or more hydraulic actuator(s) ( 36, 38 ) for the artificial hand and a high-pressure configuration in which the discharge side of the low-pressure pump ( 76 ) is isolated from the hydraulic actuator(s) ( 36, 38 ) and recirculates fluid to the suction side of the low pressure pump ( 76 ) with the discharge side of the high-pressure pump ( 74 ) remaining coupled to the hydraulic actuator(s) ( 36, 38 ), and wherein the hydraulic circuit is arranged to switch from the low-pressure configuration to the high-pressure configuration automatically during a closing grip pattern when the pressure in the system increases beyond a threshold value.

The present invention relates to a palm unit for an artificial hand, forexample a prosthetic hand used to replace a person's missing hand. Insome example embodiments the palm unit is combined with fingers to forma complete artificial hand.

There is an on-going demand for improvements in artificial hands notonly for use as prosthetics but also in relation to robotics andautomated handling devices that can mimic the dexterity of the humanhand. The last few decades have seen great advances in relation tomyoelectric artificial hands, which use electromyography signals orpotentials from voluntarily contracted muscles within a person'sresidual limb to control the movements of the hand. A sensor or multiplesensors are placed on the surface of the skin to receive the signals.Some time ago Otto Bock (Otto Bock HealthCare Deutschland GmbH ofDuderstadt, Germany, www.ottobock-group.com) designed a wrist connectorunit that has become a standard in the field of myoelectric artificialhands. Devices also exist that use electromechanical switches actuatedby body movements in order to control the artificial hand.

A review of the current state-of-the-art in relation to anthropomorphicprosthetic hands can be found in “Mechanical design and performancespecifications of anthropomorphic prosthetic hands: A review” by JosephT. Better et at, JRRD, volume 50, number 5, 2013, pages 599-618. Asdiscussed in that review, a number of companies are active in the fieldand have commercial products on the market. The commercial products makeuse of various combinations of electrical motors and mechanicalcouplings to actuate the fingers and thumb of the hand with varyingdegrees of freedom. Whilst these commercially available hands can insome cases provide a suitable level of dexterity for an artificial handfor use as a prosthetic hand they generally suffer from excessiveweight, causing discomfort for the user, and they are complex andexpensive.

Hydraulically actuated hands have also been proposed, although to dateno commercial product is known to exist. A hand design known as“Fluidhand” has been developed at the Karlsruhe Institute of Technology(KIT) as a prototype that has been tested in the Orthopaedic UniversityHospital in Heidelberg. This hand uses miniature hydraulics within thefingers in an attempt to provide a large degree of freedom of movement(and hence dexterity) in an alternative manner to the commercialelectromechanical hands. However, the “Fluidhand” is operated at arather low pressure (9 to 10 bar) and this means that the gripping forceis relatively low. Another disadvantage is the use of externally mountedhoses and couplings, which are vulnerable to damage and mean that thehand is not sufficiently robust for everyday use as a prosthetic. Thereis also a significant risk of leakage of the hydraulic fluid.

Further proposals for the use of hydraulics are found in patentpublications. US 2012/203358 discloses a mesofluidic powered fingerusing high-pressure low-volume hydraulics to actuate each individualjoint of a finger. This proposal is considered to suffer from similardisadvantages to the “Fluidhand”.

U.S. Pat. No. 8,951,303 proposes the use of hydraulics along with amechanical finger joint. The fingers are actuated by tendon cables in away similar to some of the commercially available electromechanicalprosthetic hands, and a pair of mesofluidic hydraulic pistons controlmovement of each finger joint. Although this system addresses some ofthe issues with fully hydraulic artificial hands, there are stillproblems that remain. The strength of the group that can be produced isconstrained due to the nature of the hydraulic system, and therequirement for multiple hydraulic pistons for each finger results in asignificant degree of complexity leading to costly production and a riskof leakage.

Another example of a combination of hydraulic and mechanical elements isfound in WO 2011/072750, which describes a hand having mechanical tendoncable actuated finger joints moved via a single hydraulic piston foreach finger. In order to allow for both a fast finger movement and highgrip strength WO 2011/072750 proposes the use of two hydraulic pumpsproviding the possibility of high pressure and low pressure operation ofthe hydraulic elements. The lower pressure hydraulic pump is decoupledfrom the motor/hydraulics via a clutch and isolating valve in order toallow the high pressure hydraulic pump to control the finger movement.The system is arranged to do this automatically when the grippingpressure increases above the threshold. This hand will hence begin witha fast movement to bring the fingers into contact with an object at alower gripping pressure, and then switch to a slower higher pressuremovement to increase the strength of the grip. In addition, the variouspistons that actuate the fingers are all coupled together and this meansthat the different fingers will close to a different degree depending onthe resistance that they meet from a gripped object as the pressure ismaintained equally across each hydraulic piston, and the greatestgripping force on the object is not applied until all of the fingershave closed about the object.

The hand disclosed in WO 2011/072750 is considered to represent asignificant advance compared to other known hydraulically poweredartificial hands, but it still suffers from potential problems. The handis relatively bulky and complex and yet still does not providesignificant advances in the control of finger movement for the user.Hence there remains a need for improvements in relation to artificialhands of this type.

Viewed from a first aspect, the present invention provides a palm unitfor an artificial hand, the palm unit comprising: a palm unit body; amotor held by the palm unit body; a hydraulic pump assembly held by thepalm unit body and comprising a low-pressure hydraulic pump and ahigh-pressure hydraulic pump, wherein both hydraulic pumps are poweredsimultaneously by the motor; and a hydraulic circuit held by the palmunit body and coupled to both hydraulic pumps, wherein the hydrauliccircuit has a low-pressure configuration in which the discharge sides ofboth hydraulic pumps are coupled to one or more hydraulic actuator(s)for the artificial hand and a high-pressure configuration in which thedischarge side of the low-pressure pump is isolated from the hydraulicactuator(s) and recirculates fluid to the suction side of the lowpressure pump with the discharge side of the high-pressure pumpremaining coupled to the hydraulic actuator(s), and wherein thehydraulic circuit is arranged to switch from the low-pressureconfiguration to the high-pressure configuration automatically during aclosing grip pattern when the pressure in the system increases beyond athreshold value.

The above arrangement provides a palm unit capable of effective controlof an artificial hand both with a fast low-pressure movement and a slowhigh-pressure movement, with the switching between low strength and highstrength being automatic in reaction to pressure building up in thesystem, which advantageously can allow the system to automatically reactto resistance when the artificial hand is gripping an object. Incontrast to the system described in WO 2011/072750 there is no need fora mechanical clutch and an additional isolation valve in order todecouple the low-pressure pump when it is required to run the systemwith the high-pressure pump alone. Counter intuitively, the systembecomes quieter and more effective when the low-pressure pump is allowedto continue to operate in a recirculating mode, rather than fullydecoupling it from the motor and the hydraulic circuit. The absence of amechanical clutch also allows reductions in the size and weight of thesystem and the use of fewer moving parts, giving increases inreliability. Reductions in size and weight are important in particularin relation to prosthetic hands since it allows for lesser amputees tomake effective use of the hand, increases comfort of the patient, andincreases the range of age and size of patient that can effectively usethe hand.

In order to switch from the low-pressure configuration to thehigh-pressure configuration automatically when the pressure in thesystem increases beyond a threshold value the hydraulic circuit mayinclude a pressure controlled mechanism, for example a pressurecontrolled valve arranged to open when the pressure increases beyond thethreshold value whilst the user is closing the hand. The threshold valuemight be a value between 10 and 15 bar, for example.

In one example hydraulic circuit the discharge side of the low-pressurepump is coupled to the discharge side of the high-pressure pump via aone-way valve permitting flow from the low-pressure pump toward thehigh-pressure pump and the discharge side of the low-pressure pump iscoupled to the suction side of the low-pressure pump via the pressurecontrolled valve. With this arrangement, when the pressure at thedischarge side of the low-pressure pump increases above the thresholdvalue then the pressure controlled valve will open allowing for fluid torecirculate from the discharge side of the low-pressure pump to thesuction side of the low-pressure pump, and resulting in closure of theone-way valve due to the higher pressure at the discharge side of thehigh-pressure pump. This means that discharge side of the high-pressurepump will remain coupled to the hydraulic actuators as required, whereasthe low-pressure pump will be switched to operating in a recirculatingmode.

It is preferred for the one-way valve to be able to be held open, forexample to allow for reverse flow of fluid through the circuit duringopening of the hand. The one-way valve may be an electromagnetcontrolled valve. The palm unit may include a controller such as amicroprocessor for controlling the electromagnet controlled valve. Thiscan be utilised to hold the valve open, for example when opening thehand requires reverse movement of hydraulic fluid through the circuit.

The motor may be a variable speed motor. This allows the user to controlthe volume of fluid pumped by the hydraulic pumps with only a singlesensor input, and hence the user can have complete control of the speedof operation of the hand without the need for multiple sensors and/orcomplicated microprocessor routines. The use of a variable speed motorin conjunction with a hydraulic circuit having two operating pressuresis considered novel and inventive in its own right and hence, viewedfrom a second aspect, the invention provides a palm unit for anartificial hand, the palm unit comprising: a palm unit body; a motorheld by the palm unit body; a hydraulic pump assembly held by the palmunit body and comprising a low-pressure hydraulic pump and ahigh-pressure hydraulic pump, wherein both hydraulic pumps are poweredsimultaneously by the motor; and a hydraulic circuit held by the palmunit body and coupled to both hydraulic pumps, wherein the motor is avariable speed motor. This gives the advantages above, which are notpossible with prior hydraulic hands such as the hand described in WO2011/072750. The palm unit of this aspect may be combined with thefeatures of that any of the other aspects as well as any of the optionaland preferable features described herein.

A reversible motor may be used, thereby permitting close control by theuser of opening and closing of the hand by forward and reverse operationof the hydraulic pumps. The use of a reversible motor in conjunctionwith a hydraulic circuit having two operating pressures is alsoconsidered novel and inventive in its own right and hence, viewed from athird aspect, the invention provides a palm unit for an artificial hand,the palm unit comprising: a palm unit body; a motor held by the palmunit body; a hydraulic pump assembly held by the palm unit body andcomprising a low-pressure hydraulic pump and a high-pressure hydraulicpump, wherein both hydraulic pumps are powered simultaneously by themotor; and a hydraulic circuit held by the palm unit body and coupled toboth hydraulic pumps, wherein the motor is a reversible motor. The palmunit of this aspect may be combined with the features of that any of theother aspects as well as any of the optional and preferable featuresdescribed herein.

Preferably the motor is both variable speed and reversible.

Typically there would be multiple hydraulic actuators, for example toallow for control of one or more fingers and the thumb. Preferably thehydraulic circuit is arranged so that the pressure and suction side ofeach of the hydraulic actuators is linked to equalise the pressure inthe hydraulic fluid within multiple actuators, preferably within allactuators. This allows for adaptive movement of individual fingers andthe thumb, whereby the finger or thumb will stop when it meetsresistance with other fingers or the thumb continuing to move until thegrip is completed.

In preferred embodiments there are fewer hydraulic actuators than thenumber of fingers and thumbs on the hand. Naturally, the artificial handwould typically be arranged to have four fingers and one thumb. Theremay hence be fewer than five actuators. The feature of omitting to havehydraulic actuators for all fingers and thumbs is considered novel andinventive in its own right and hence, viewed from a fourth aspect, theinvention provides a palm unit for an artificial hand, the palm unitcomprising: a palm unit body; a motor held by the palm unit body; ahydraulic pump assembly held by the palm unit body and comprising alow-pressure hydraulic pump and a high-pressure hydraulic pump, whereinboth hydraulic pumps are powered simultaneously by the motor; and ahydraulic circuit held by the palm unit body and coupled to bothhydraulic pumps, wherein the hydraulic circuit includes hydraulicactuators for movement of fingers and thumbs of the artificial hand andwherein there are fewer hydraulic actuators than the number of fingersand thumbs. The palm unit of this aspect may be combined with thefeatures of that any of the other aspects as well as any of the optionaland preferable features described herein.

Preferably the palm unit does not include a separate hydraulic actuatorfor the little finger and optionally also it does not include a separatehydraulic actuator for the ring finger. In some examples the fingerswithout their own hydraulic actuator are resiliently coupled to anadjacent finger which does have an actuator. For example, the littlefinger and ring finger may be resiliently coupled to the middle finger,with the middle finger having a dedicated hydraulic actuator. In apreferred arrangement the palm unit includes three hydraulic actuators,being for the thumb, the index finger and the middle finger. Thisarrangement is in contrast to WO 2011/072750 which has hydraulicactuator for each of the fingers. It has been found that there is nosignificant disadvantage in terms of grip pattern when the little fingerand optionally the ring finger are not provided with their own dedicatedhydraulic actuator, and that any disadvantages outweighed by theadvantage in reductions in size, weight and complexity of the artificialhand. The hydraulic actuators may be hydraulic cylinders.

In a preferred embodiment the hand includes a hydraulic cylinder for thethumb and multiple hydraulic cylinders for the fingers, and the boresize of the hydraulic cylinder for the thumb is larger than the boresize for the hydraulic cylinders of the fingers. Preferably the boresizes are set so that the force that can be applied by the thumb isbalanced with the forces from each of the fingers combined. This meansthat when the hand is closed then the force from the thumb side of thegrip will balance with the force from the finger side of the grip.

The high-pressure pump may be arranged to operate at relatively lowvolumes and the low-pressure pump may be arranged to operate atrelatively high volumes. This enables a quick low strength movement anda slow high-strength movement, which mimics natural use of the hand whengripping an object.

The hydraulic pump assembly may be formed as a single unit includingboth hydraulic pumps and being arranged to fit within a single chamberin the palm unit. This feature provides advantages in relation to thesize and weight and it is considered novel and inventive in its ownright and hence, viewed from a fifth aspect, the invention provides apalm unit for an artificial hand, the palm unit comprising: a palm unitbody; a motor held by the palm unit body; a hydraulic pump assembly heldby the palm unit body and comprising a low-pressure hydraulic pump and ahigh-pressure hydraulic pump, wherein both hydraulic pumps are poweredsimultaneously by the motor; and a hydraulic circuit held by the palmunit body and coupled to both hydraulic pumps, wherein the hydraulicpump assembly is a single unit including both the high-pressure and thelow-pressure hydraulic pump, and this single unit is arranged to fitwithin a single chamber in the palm unit. The palm unit of this aspectmay be combined with the features of that any of the other aspects aswell as any of the optional and preferable features described herein.

The hydraulic pump assembly may be arranged with a prismatic shape forfitting into a chamber in the palm unit with a corresponding prismaticshape. A preferred arrangement uses a cylindrical shape for ease ofmanufacture and ease of assembly, as well as in order to ensure that agood seal can be obtained.

Preferably the pump assembly is sealed from the outside world within thepalm unit. The pump assembly may include a seal, or a groove for holdinga seal, at one end of the hydraulic pump assembly. This allows theentire hydraulic pump assembly to be accurately sealed within thechamber in the palm unit. The seal may for example be an O-ring typeseal. By fully sealing the pump assembly within the palm unit it becomespossible to dispense with some of the seals that would otherwise berequired between the two parts of the pump assembly since any leakagewould be internal and therefore does not create a problem. Thedisadvantage of potential internal leakage is outweighed by theadvantage in the reduction in size and weight of the pump, which asnoted above is highly important for an artificial hand. In one examplethe pump assembly includes a hydraulic axle seal for the shaft betweenthe two pumps, but does not include any seals between pump plates of thepumps.

Preferably both of the hydraulic pumps are actuated by a single driveshaft assembly powered by the motor. This feature also providessignificant advantages in terms of size and weight and again and it isconsidered novel and inventive in its own right and hence, viewed from asixth aspect, the invention provides a palm unit for an artificial hand,the palm unit comprising: a palm unit body; a motor held by the palmunit body; a hydraulic pump assembly held by the palm unit body andcomprising a low-pressure hydraulic pump and a high-pressure hydraulicpump, wherein both hydraulic pumps are powered simultaneously by themotor; and a hydraulic circuit held by the palm unit body and coupled toboth hydraulic pumps, wherein the hydraulic pump assembly includes asingle drive shaft assembly for powering both the high-pressure and thelow-pressure hydraulic pumps. The palm unit of this aspect may becombined with the features of that any of the other aspects as well asany of the optional and preferable features described herein.

The drive shaft assembly may include a shaft passing along an axis ofthe pump assembly. Thus, a shaft powered by the motor may pass throughone of the pumps in order to reach the other pump. This shaft may besplit in two, having a low-pressure section and high-pressure sectiondriving the respective hydraulic pump, with axial play between the twosections. This has the advantage that the mechanical elements of thepump are axially isolated from one another.

In a preferred embodiment the pump assembly is assembled from a numberof pump plates assembled together and held with bolts extending throughthe length of the pump assembly. Preferably the shaft also passesthrough the length of the pump assembly through the pump plates. Thepump assembly may be generally cylindrical in form and it may bearranged to be inserted within a cylindrical chamber in the palm unit.The sealing between the pump and the outside world may be provide by anO-ring type seal or similar.

The palm unit body may form a sealed enclosure for the hydraulic circuitand hydraulic pump assembly, thereby containing all hydraulic parts.Preferably the motor is also contained within the palm unit body. Thepalm unit body is preferably formed in a single piece and in a preferredexample it is formed by 3-D printing. This construction for the palmunit is considered to be novel and inventive in its own right. Thus,viewed from a seventh aspect, the invention provides a palm unit for anartificial hand, the palm unit comprising: a palm unit body; a motorheld by the palm unit body; a hydraulic pump assembly held by the palmunit body and powered by the motor; and a hydraulic circuit held by thepalm unit body, wherein the palm unit body forms a sealed enclosure forall hydraulic parts including the hydraulic circuit and hydraulic pumpassembly, and wherein the palm unit body is formed in a single piece,preferably by 3-D printing. The palm unit of this aspect may be combinedwith the features of that any of the other aspects as well as any of theoptional and preferable features described herein. For example, the pumpassembly may comprise a low-pressure hydraulic pump and a high-pressurehydraulic pump, wherein both hydraulic pumps are powered simultaneouslyby the motor.

It is preferred for all hydraulic connections for the hydraulic circuitto be formed by channels within a single piece palm unit body. Thisincludes connections between the hydraulic pumps and hydraulicactuator(s), as well as for the various valves mentioned above (ifpresent). This arrangement is particularly effective when combined with3-D printing since the use of 3-D printing allows a very complicatedshape to be formed with numerous internal features. By retaining allhydraulic connections between the various parts within the palm unitbody it becomes straightforward to fully seal all hydraulic elements andensure that the hydraulic system is robust and not at risk of damage orleakage.

The hydraulic circuit may include a locking valve in order to holdpressure within the hydraulic actuators when the motor has stopped.Advantageously this can allow for the palm unit to maintain the fingersand thumb in a locked grip position without the need to run the motorcontinually.

Preferably the palm unit is arranged to operate based on inputs frommyoelectric sensors such as EMG sensors. In a preferred embodiment thelevel of tension in the user's muscle is used to control motor speed,which means that a single sensor can provide a great degree of controlof the grip from the hand. This can avoid the need for a complicatedprogrammable microprocessor. In one preferred example the palm unit isarranged to operate based on inputs from two EMG sensors, one of whichis actuated to open the hand and the other of which is actuated to closethe hand.

The palm unit may include a wrist connector. In particular it ispreferred to use a quick connect type wrist connector. An Otto Bock typequick connect may be used. Using this type of standard connector allowsthe hand to be easily tried out by existing users of prosthetic hands.The invention further extends to an artificial hand including a palmunit as described above along with artificial fingers and a thumb. Theartificial hand may be a prosthetic hand and hence may include acosmetic glove. The fingers and thumb could potentially be fullyhydraulic, but for the reasons set out above this is considered to be adisadvantage. Consequently, it is preferred for the fingers and thumb tohave mechanical joints arranged to be actuated by hydraulic actuatorswithin the palm unit, but not including any hydraulic elementsthemselves. This combination of mechanical fingers and thumb with ahydraulic palm unit is considered to provide the optimum design forminimal size and weight. There are currently no commercially availablehands that use a combination of hydraulic and mechanical elements inthis way.

The palm unit of any of the aspects described above may be combined witha digit mechanism for an artificial hand, preferably a digit mechanismthat provides an adaptive grip, i.e. digit movements that adapt based onthe gripped objects. One possible digit mechanism comprises: a lowerdigit arranged to be rotatably coupled to a palm unit of the artificialhand; an upper digit rotatably coupled to the lower digit; a lower digitrotation mechanism for applying a moment to the lower digit to rotatethe lower digit relative to the palm unit; an upper digit rotationmechanism for applying a moment to the upper digit to rotate the upperdigit relative to the lower digit; and a force balancing mechanism formechanically adjusting the magnitude of the moment applied by the lowerdigit rotation mechanism and/or the upper digit rotation mechanism inaccordance with the magnitude(s) of outside forces resisting rotation ofthe upper digit and/or the lower digit in order to preferentially applymovement to the digit experiencing lower resistance to movement; whereinthe lower digit rotation mechanism and upper digit rotation mechanismare arranged to be mechanically actuated, in use, by a force appliedfrom a single actuator at the palm unit.

With this arrangement the digits can be controlled for an adaptive gripwith only a single actuator at the palm unit applying a single force tothe digit mechanism. When one of the digits meets with increasingresistance then the force balancing mechanism adjusts the distributionof forces so that the other digit receives a greater proportion of theforce supplied to the digit mechanism, and is therefore rotatedrelatively more. In this way it becomes possible to ensure that bothdigits move to come in contact with an object, even when the object isof an irregular shape, for example to close the digits around an objectwhen an artificial hand using the digits is gripping the object. Themechanism may be set with a default pattern of movement when there is noresistance to rotation of the digits, for example in order to close thehand using the digit mechanism into a pincer grip, and when the firstdigit comes into contact with an object to be gripped or with anothersource of resistance to movement then the proportion of force suppliedto that digit is reduced compared to the amount of force supplied to theremaining digit, thereby ensuring that both digits will close againstthe resistance to movement with generally equal pressure. This ensuresthat a firm grip can be achieved in a similar way to a natural hand,with the digit mechanism making use of all of the digits to form thegrip. It also means that the user can very easily “shape” an artificialhand into a required grip pattern or pose by selectively resisting themotion of different digits using the above digit mechanism.

Unlike known digit mechanisms with adaptive capabilities there is noneed for multiple actuators and complicated microprocessor control.Instead, a single actuator can be used. In addition, in contrast toknown digit mechanisms using a single actuator input and tendon typeconnections, the relative degree of movement of the upper and lowerdigits can vary and is not fixed by gearing or the like. The proposeddigit mechanism also allows for a much more robust construction, and inparticular the ability to introduce a spring back type arrangement.Thus, the digit mechanism may be arranged to flex in response to outsideforces and to be able to be pushed and moved in the closing directionresiliently, thereby minimising the risk of damage to the digitmechanism and other elements of an artificial hand in which it may beincorporated.

As used herein, the term upper digit references a digit of theartificial finger or thumb closer to its distal end, i.e. closer to thetip of the finger or thumb, and the term lower digit references a digitof the finger or thumb at the proximal end, i.e. closest to the palm.The terms upper and lower are used in a similar way below to refer toother parts of the mechanism. The digit mechanism may form the basis fora finger or a thumb of the artificial hand.

There may be just two moveable digits in the digit mechanism and in thatcase the upper digit is the distal digit and would move with the tip ofthe finger or thumb. It would be possible to expand to have three digitsby adding a further rotation mechanism and a further force balancingmechanism described below so that a further digit was included betweenthe lower digit and the uppermost digit. Thus there may be a lowerdigit, a first upper digit rotatably coupled to the lower digit at alower end of the first upper digit, and a second upper digit rotatablycoupled to an upper end of the first upper digit, with an additionalrotation device for applying a moment to the additional upper digit andan additional a lower pulley as described above, a first upper pulleyinteracting with the lower pulley and a first clutch mechanism providedat the lower pulley as described above, and also a second clutchmechanism at the first upper pulley interacting with a second upperpulley and other repeated elements to create a further system foradaptive movement of the second upper digit. This allows for movement ofthree digits as with a natural finger and thereby may allow for an evenmore natural adaptive finger movement.

In order to generate the required adaptive grip the force balancingmechanism mechanically adjusts the magnitude of the moment applied bythe lower digit rotation mechanism and/or the upper digit rotationmechanism in accordance with the magnitude(s) of outside forcesresisting rotation of the upper digit and/or the lower digit and as aresult the two rotation mechanisms preferentially apply movement to thedigit experiencing lower resistance to movement. This may be achieved byincreasing the force applied to rotate a controlled digit when acontrolling digit experiences a greater resistance to movement than thecontrolled digit, and decreasing the force applied to rotate thecontrolled digit when the controlling digit experiences a lesserresistance to movement than the controlled digit. The controlling digitmay be the upper digit and the controlled digit the lower digit, or viceversa. The first option is used in an example embodiment describedherein. With the typical geometry required for an artificial hand thatfollows the aesthetics of the human hand then there is more spaceavailable for installation of mechanisms at the proximal end, and sincein general a more complex mechanism is required to adjust the amount offorce applied to rotate a digit than to react to the amount of forcethat resists rotation of digit then an arrangement using the lower digitas the controlled digit can more easily be designed without adverseimpact on the aesthetics of the artificial hand. There is hence a slightadvantage to arranging the mechanism in that way.

The force balancing mechanism may include a clutch for transmission of avarying amount of power for rotation of the controlled digit with theclutch being controlled to adjust the varying amount of power inaccordance with the degree of resistance to motion of the controllingdigit. The use of a clutch in this way allows for an effective controlof the proportion of power used to move one digit as compared to theother. To control the clutch the force balancing mechanism may include aclutch controller, preferably a mechanical device that is moved inaccordance with the magnitude of the resistance to movement of thecontrolling digit. In the digit mechanism since the upper digit rotationmechanism and the lower digit rotation mechanism are mechanicallyactuated then an increase in resistance to movement of a digit willincrease the forces in the respective rotation mechanism, for exampleincreasing a torque, tension, compression, and/or strain in elements ofthe mechanism. It is preferred for the clutch controller to be moved bya force of this type. In one example the digit rotation mechanism forthe controlling digit is actuated by a cable, such that increasedresistance to rotation of the digit will increase the tension in thecable. In this case the clutch controller may include a mechanicaldevice that is moved in accordance with the tension in the cable, suchas a lever that the cable passes over in a V-shape. With thisarrangement tension in the cable will tend to pull the lever, allowingthe lever to be moved in accordance with the magnitude of the resistanceto movement of the controlling digit. Other mechanisms would of coursebe possible.

The clutch may be any mechanism able to control the amount of power usedfor rotation of the controlled digit in comparison to the amount ofpower used for rotation of the controlling digit. It is preferred forthe clutch to include an adjustment/calibration mechanism so that it canbe effectively set up to achieve the required balance in forces, forexample to ensure a pincer type grip when there is no resistance tomotion as described above. A person skilled in the art will appreciatethat there are numerous ways that such clutch could be implemented. In apreferred embodiment a band brake is used. This has been found toprovide a lightweight and easily miniaturisable clutch, and these areimportant advantages for an artificial hand where, as discussed above,the size and weight are significant. A band brake as the clutch may becombined with a lever and cable arrangement of the type discussed aboveas the clutch controller, with the lever acting to tighten the bandbrake in accordance with increasing tension in the cable. This has againbeen found to be a mechanism that provides a small and lightweightsolution, as well as being robust and easily implemented within thegeometry of artificial digits. The band brake may include anadjustment/calibration mechanism as described above, for example througha screw adjuster that adjusts the tightness of the band brakeindependently of the adjustment applied by the clutch controller (forexample the lever discussed above).

The digit rotation mechanisms for the upper and lower digit may includepulley and cable systems. One possibility includes a main cable forreceiving a tension force from an actuator in the palm unit and fortransferring this to a lower pulley about which the lower digit isarranged to rotate; and a secondary cable also coupled to the lowerpulley and arranged to transfer a rotating movement of the lower pulleyto an upper pulley about which the upper digit is arranged to rotate.The main cable and the secondary cable could be formed as a single cablewrapped around the lower pulley or otherwise attached thereto. However,it is advantageous to use separate cables so that they may separately bedisconnected from the lower pulley, as this makes it easier to assemblethe device and simpler to remove different individual parts, for examplefor maintenance. The use of cables and pulleys in this way has anadvantage in that the digit can freely be pushed toward the closedposition, i.e. creating slack in the cables, without risk of damage tothe mechanism. This means that when they are mounted on a palm unit toform an artificial hand the digits are resistant to damage from impacts.

With the use of pulleys as above the force balancing mechanism may bearranged either to adjust the amount of force transferred between theupper pulley and upper digit in accordance with resistance to motion ofthe lower digit around the lower pulley, or to adjust the amount offorce transferred between the lower pulley and the lower digit inaccordance with resistance to motion of the upper digit around the upperpulley. As noted above there are considered to be advantages in havingthe force balancing mechanism constructed at the lower end of the digitmechanism, and therefore further details will be discussed in thecontext of a system focused on the lower pulley. It should beappreciated that the opposite arrangement could also be used.

When the force balancing mechanism is arranged to adjust the forcestransferred from the lower pulley to rotate the lower digit then thetension in the main cable and the secondary cable may be linked by theirconnection to the lower pulley, and the upper pulley may be coupled toand rotate with the upper digit, i.e. so that the upper digit has thesame degree of rotation as the upper pulley and is actuated by rotationof the upper pulley, with the lower pulley coupled to the lower digitwith a clutch of the force balancing mechanism for partial transfer ofthe rotation force from the lower pulley to the lower digit. The clutchmay be as described above. Thus, in one example there may be a lever asa clutch controller, with the secondary cable passing over the lever ina V shape between the lower pulley and upper pulley, such that increasedresistance to movement of the upper digit will increase the tension inthe secondary cable and pull the lever to increase the force transferredbetween the lower pulley and the lower digit by the clutch. The forcebalancing mechanism may include a band brake as the clutch in this case,with the band brake being arranged to control the amount of forcetransferred between the lower pulley and the lower digit; and the leveracting to tighten the band brake. Advantageously, the band brake andlower pulley can be accommodated in a relatively large “knuckle” at thelower end of the lower digit, with the lever and the V-shaped cablebeing placed within the lower digit extending toward the upper pulley,which is accommodated in a relatively small “knuckle” where the lowerdigit and upper digit join each other. The digit mechanism can includethese features without needing to be oversized compared to a normalartificial hand, i.e. whilst being able to generally match the size ofthe digits of the patient's natural hand.

The digits may include housing elements formed as hollow digit-likeshapes. A preferred example uses 3-D printed metal alloy, for example3-D printed titanium, in order to form the digits. This provides therequired structural strength whilst also allowing for complex shapeswhich minimise the need for additional machining when manufacturing thedigit mechanism and fitting the various mechanical parts together.

Multiple digit mechanisms as described above may be mounted to a palmunit. The palm unit may include actuators for the digit mechanisms, forexample actuators arranged to apply tension to main cables of the digitmechanisms or to otherwise apply rotation to the digits. The combinationof mechanical fingers and thumb with a hydraulic palm unit is consideredto provide the optimum design for minimal size and weight. There arecurrently no commercially available hands that use a combination ofhydraulic and mechanical elements in this way.

Preferably the digit mechanism includes an attachment point for a springthat, in use, urges the digit towards the open position. The spring maybe mounted between the attachment point and a corresponding attachmentpoint on the palm unit of the artificial hand. The spring allows for thedigits to be resiliently pushed toward the closed position, returning tothe open position when any forces are released. The digits can hence bearranged to freely close in relation to an impact or other outsideforce, and to then return to the open position (or to a position set bythe relevant actuator) when the outside force is removed.

The lower digit may include a pivot arrangement for mounting to abracket on a palm unit of the artificial hand, and preferably the pivotarrangement is formed along the same axis of rotation as elements of thelower digit rotation mechanism, for example the lower pulley and clutchas described above. The digit mechanism may be mounted to the palm unitvia coupling of the pivot arrangement to a bracket on the palm unit.Advantageously, multiple digit mechanisms for the fingers may be mountedto brackets that are aligned along the same axis of rotation, therebyallowing a single pin or shaft to secure all of the fingers to the palmunit.

The use of 3-D printing is considered a particular advantage. Hence,further aspects of the invention include methods for manufacture of apalm unit as described above in any of the aspects or preferred/optionalfeatures thereof, the method comprising using 3-D printing to form thepalm unit body, preferably as a single piece. The invention furtherextends to 3-D printing source files, and computer media including thosesource files, the 3-D printing source files containing instructionsthat, when executed will configure a 3-D printing apparatus to form thepalm unit body of a palm unit as described above in any of the aspectsor preferred/optional features thereof.

Preferred features of each aspect of the invention may be combined withthe other aspects of the invention, and optionally with preferredfeatures of the other aspects, as far as is applicable or appropriate.

Certain preferred embodiments of the invention will now be described byway of example only and with reference to the accompanying drawings inwhich:

FIG. 1 shows a design for a prosthetic hand in perspective view with thecosmetic glove removed and one finger shown partially transparent sothat internal detail can be seen;

FIG. 2 is a partial cutaway view of the prosthetic hand of FIG. 1showing a cross-section through the hydraulic cylinders for the middlefinger and for the thumb;

FIG. 3 shows a finger mechanism in more detail illustrating a clutchsystem for producing adaptive movement with the finger joints;

FIG. 4 is a schematic diagram showing the basic principles of operationof the clutch system;

FIG. 5 is a perspective view of the palm unit with the outer housingshown transparent so that internal detail of the motor and hydraulicpumps can be seen;

FIG. 6 is a partial cross-section through the palm unit showing the highand low pressure hydraulic pump and equaliser adjacent to the hydrauliccylinder for the thumb;

FIG. 7 shows a similar cross-section to FIG. 6, from a different angle,with the hydraulic pump assembly removed so that the hydraulic pumppressure and suction channels can be seen;

FIG. 8 is a perspective view of a hydraulic subassembly of the palm unitwith the finger joints at the upper part and the thumb joint at thelower part and also showing the location of an emergency hydraulicvalve;

FIG. 9 shows the emergency valve in more detail with the outer part ofthe hydraulic subassembly shown transparent for clarity;

FIG. 10 is a hydraulic schematic;

FIGS. 11 and 12 show a cross-section and perspective view of a hydrauliccylinder for the index and middle fingers;

FIGS. 13 and 14 shows similar views for a hydraulic cylinder for thethumb;

FIGS. 15 and 16 show the emergency valve in cross-section andperspective view;

FIGS. 17 and 18 show more detail of an equaliser that is seen in situ inFIG. 5 and FIG. 6;

FIGS. 19 and 20 show a cross-section and perspective view for the highand low pressure hydraulic pumps, which again are already seen in situin FIG. 5 and FIG. 6;

FIGS. 21 and 22 show a cross-section and perspective view for a pressurecontrolled valve that redirect the oil flow to switch from low-pressureto high pressure operation;

FIGS. 23 and 24 are a cross-section and perspective view of a design foran electromagnet controlled valve used within the hydraulic circuit;

FIG. 25 shows a 3-D printed body section for the hydraulic subassemblyshown in FIG. 8; and

FIG. 26 shows a cutaway view of the body section illustrating some ofthe hydraulic connections.

By way of a preferred embodiment the drawings show a prosthetic hand andvarious features of the mechanisms used to produce finger and thumbmovements for this prosthetic hand. It will however be appreciated thatthe same mechanisms could equally well be used in artificial hands forother purposes, for example for remote handling or in roboticapplications. In addition, it will be noted that whilst there areparticular advantages to the various features of the hand when taken incombination as shown in the Figures, there are also advantages thatwould arise when the different features of the hand are taken alone, forexample the arrangement of the finger joint as described herein wouldprovide advantages when used with alternative driving mechanisms and notjust the hydraulic driving mechanism with the particular arrangement ofthe current palm unit, and similarly the palm unit and/or hydrauliccircuit described herein would provide advantages when used with analternative arrangement for the finger and thumb mechanisms.

Considering the Figures in more detail, FIG. 1 shows a perspective viewfor a prosthetic hand including a palm unit 12 a thumb mechanism 14, anindex finger mechanism 16, a middle finger mechanism 18 and a combinedring finger/little finger mechanism 20. FIG. 2 shows a partial cutawayview with a slice taken along the line of the thumb 14 and between theindex finger 16 and middle finger 18.

In this example the hand is provided with a standard quick connect OttoBock design wrist joint 22 that allows for coupling with batteries andone or two electromyocardiographic (EMG) sensors, which would typicallybe mounted inside the user's underarm. It would of course be possible toadapt the hand to use an alternative wrist connection system ifrequired. Advantageously, the coupling for the wrist joint 22 is 3-Dprinted. The use of a standard quick connect system 22 makes it possiblefor an existing electric hand prosthetic user to try this hand veryeasily.

The index finger mechanism 16 and the middle finger mechanism 18 arevery similar and differ generally only in relation to the size of thefingers. The thumb mechanism 14 is similar to the finger mechanisms 16,18 with the addition of a pulley/guide 24 directing the main cable 34about an angle to allow for the thumb 14 to open at 90° to the fingers16, 18, 20, and of course with some changes in size and dimensions so asto accurately mimic typical dimensions for a thumb. The ringfinger/little finger mechanism 20 is resiliently coupled to andeffectively slaved with the mechanism for the first digit of the middlefinger mechanism 18. In this example a coiled spring is used, and thisis advantageously fitted with a bushing allowing for a sprung movementof the little and ring fingers whilst opening, within limits, and a freemovement (resisted by the spring, but without any restriction on theextent of movement) in the closing direction.

Microprocessor control electronics and software are provided tointerpret the signals from the user's EMG sensors. These electronics aremounted behind the quick connect 22 inside the palm unit 12, i.e. withinthe right hand side of the palm unit 12 when viewed in the orientationof FIG. 2. It is important to understand that this hand design canoperate with just a single sensor input if necessary, and based solelyon the “strength” of this signal it is possible to achieve a veryadaptable grip controlled by the user, as explained in more detailbelow. The use of a second EMG sensor is preferred since it allows for amore intuitive action of the user in releasing the grip of the device:one sensor can be used to control closing of the hand, and the othersensor will control opening of the hand. However, if necessary a singlesensor can be used along with a prearranged signal for switching fromclosing to opening of the hand, for example a “double click” typemovement. Further detail of the construction and operation of the thumband finger mechanisms 14, 16, 18 will be discussed below with referenceto FIG. 3 and FIG. 4 and the relevant reference numerals are not shownin FIG. 1 and FIG. 2 for the sake of clarity. In FIGS. 1 and 2 furtherdetail of the basic parts of the palm unit 12 can be seen including thebelt 28 that couples the motor 68 to the hydraulic pumps (shown infurther detail in FIG. 5 and FIG. 6 amongst others); finger returnsprings 30, which are connected at the base of the finger joints andurge the hand toward an open configuration; finger piston couplings 32,which join the finger main cables 34 to the finger hydraulic cylinders36; the finger hydraulic cylinder 36 for the middle finger mechanism 18(in cross-section in FIG. 2); the thumb hydraulic cylinder 38 (again incross-section in FIG. 2) and thumb piston coupling 40; and the thumbreturn spring 42. The operation and interaction of these variousfeatures will be obtained from the discussion below and from thedrawings.

Turning now to FIGS. 3 and 4, which show a finger mechanism in greaterdetail, it should first be noted that the same basic functional partsare used for both the index finger mechanism 16 and middle fingermechanism 18, as well as also for the thumb mechanism 14, withappropriate adjustments to achieve the required difference in size forthe different fingers and the thumb. Thus, in the discussion belowreferences to the fingers and finger joints can be taken to applyequally well to the thumb and thumb joints.

In this explanation the upper digit is the digit of the finger or thumbat the distal end, i.e. closest to the fingertip, and the lower digit isthe digit of the finger or thumb at the proximal end, i.e. closest tothe palm, and the terms upper and lower are used in the same way torefer to other parts of the mechanism. This example uses two digits foreach of the index finger and middle finger mechanisms 16, 18 and for thethumb mechanism 14. It would be possible to expand to have three digitsby repeating the mechanism described below for a third joint of thefinger and to thereby obtain an even more natural finger movement.However, this is considered to add additional complexity without anysignificant benefit in relation to usability and the grip patterns thatcan be achieved.

FIG. 3 shows detail of a finger joint with the outer housing showntransparent so that the internal mechanism can be understood. FIG. 4shows a part of the mechanism in schematic form, with equivalent partsgiven the same reference numbers.

A lower digit 44 is connected to the palm unit 12 (not shown in theseFigures) via a pivot along a lower axis of rotation 46. The fingerreturn spring 30 is positioned so as to urge the lower digit 44 backtowards the open position, rotating it around the lower axis of rotation46. At the distal end of the lower digit 44 and upper digit 48 isconnected and can rotate relative to the lower digit 44 via a pivotalong an upper axis of rotation 50. The finger main cable 34 is attachedto a lower pulley 52 placed on the lower axis of rotation 46 and tensionon the finger main cable 34 will rotate the lower pulley 52 in order torotate the finger towards a closed position, with an adaptive grip asdiscussed below. In the view in FIGS. 3 and 4 shown this rotation wouldbe in an anticlockwise direction.

It is important to allow for rotation of both the upper digit 48 and thelower digit 44, and advantageously this is done in such a way so as toprovide an adaptive grip that can react to pressure on either one of thedigits 44, 48. This is in contrast to various prior art arrangementsthat have a fixed mechanical relationship between the various digits infinger joint, requiring that the upper digit rotate in proportion torotation of the lower digit. With the current design when the fingermain cable 34 is pulled by the actuating mechanism (the piston connectorof the finger hydraulic cylinder in this example) then this rotates thelower pulley 52 which applies tension to a secondary cable 54 that isconnected to an upper pulley 56. The upper pulley 56 is mounted on theupper axis of rotation 50 and arranged such that rotation of the upperpulley will rotate the upper digit 48, pulling it toward the closedposition (again, an anticlockwise rotation in the orientation shown inthe Figures).

In order to achieve the required adaptive grip the current joint designuses a brake/clutch arrangement 58 to transfer rotational forces fromthe lower pulley 52 to the lower joint 44 in accordance with the tensionin the secondary cable 54. The brake/clutch arrangement 58 allows for adegree of slipping in the system, so that either one digit can rotatewhilst the other digit has stopped moving. The strength of the forcesapplied via brake/clutch arrangement 58 varies dependent on the balanceof forces on the digits. Thus, in situations where there is lessresistance to the closing motion of the upper digit 48 then there willbe a reduced force closing the lower digit 44, whereas when there isincreased resistance to the closing motion of the upper digit 48 thenthere will be an increased force closing the lower digit 44. Thebrake/clutch arrangement 52 and the various pulleys are arranged so thatif there is no resistance to closing motion of the upper digit 48 orlower digit 44 then both digits will pull close with a similar degree ofrotational motion resulting in a pincer grip pattern. However, when anyone digit meets with resistance, i.e. when it contacts an object that isto be gripped, then its movement is stopped and forces are transferredpreferentially to the other digit of that finger joint, which willcontinue to move until it meets with a similar resistance. When all ofthe digits are in contact with an object then the pressure will increaseand therefore the strength of grip will also increase. The mechanismhence balances torques between the upper digit 48 and lower digit 44ensuring that each finger mechanism 16, 18 (and likewise the thumbmechanism 14) provides an intuitive adaptive grip with a greatflexibility in the grip pattern that can be achieved, whilst onlyrequiring a single actuator input in the form of tension on the maincable 34.

In this example the brake/clutch arrangement 58 is a band brake. Itwill, however, be apparent that this band brake could be replaced byalternative designs for a brake/clutch arrangement 58, such as a systemusing clutch plates. The brake/clutch arrangement 58 is coupled to atorque balancing mechanism 60 that arranged so that as the tension inthe secondary cable 54 increases then the brake/clutch arrangement 58transfers increased forces between the lower pulley 52 and the lowerdigit 44. In this example the torque balancing mechanism 60 comprises alever arm 62 attached to a pivot 64 that is fixed relative to the loweraxis of rotation 46 and fixed relative to the main body of the lowerdigit 44. This is shown schematically in FIG. 4. The end of the leverarm 62 presses against the secondary cable 54, with the secondary cable54 going through a change in direction around a guide surface at the endof the lever arm 62, such that tension in the secondary cable 54 willgenerate a force pushing the end of the lever arm 62.

When the lower pulley 52 is pulled by the main cable 34 (not shown inFIG. 4) and rotates in the anticlockwise direction then tension isapplied along the secondary cable 54 and the upper pulley 56 also tendsto rotate in an anticlockwise direction. As noted above, with noresistance to motion then the brake/clutch arrangement 58 is set so thatboth the lower digit 44 and the upper digit 48 both rotate to form apincer grip pattern. If there is resistance to motion of the upper digit48, for example through a contact force applied with the direction A atthe fingertip, then the tension in the secondary cable 54 wouldincrease. As will be understood from FIG. 4 this increased tension willhave the effect of pushing the end of the lever arm 62 with a greaterforce in the direction B, hence applying a moment to the lever arm 62around its pivot 64.

FIG. 3 shows further detail of the connections between the lever arm 62and the brake/clutch arrangement 58, i.e. the band brake in thisexample. Movement of the lever arm 62 increases forces on the band brakethereby increasing transfer of forces between the lower pulley 52 andthe lower digit 44, creating a tendency for the lower digit 44 to beclosed in preference to closing of the upper digit 48. If there werealso resistance to movement of the lower digit 44 then increasingresistance of this type would result eventually in balancing of theforces as pressure increased via the main cable 34, so that both digitswill apply pressure to increase the strength of the grip when there isfull contact of both digits with an object. If there is resistance tomotion of the lower digit 44 with less resistance to motion of the upperdigit 48 then the lower digit 44 will cease to rotate and the upperdigit 48 will continue to rotate, with a high degree of slipping of thebrake/clutch arrangement 58 which at this point would be transferringrelatively low forces between the lower pulley 52 and the lower digit44. The mechanism described above therefore provides the requiredintuitive and adaptive movement of each of the finger and thumbmechanisms 14, 16, 18.

Further adaptability of the grip pattern provided by the hand comes fromthe fact that the two finger hydraulic cylinders 36 and the thumbhydraulic cylinder 38 are coupled together with equal pressure, as canbe seen in the cross-section drawing in FIG. 2 and the hydraulicschematic of FIG. 10, for example. As a result then as well as aresistance on individual digits affecting the pattern with which anindividual finger or thumb mechanism closes, then varying resistancebetween the different finger and thumb mechanisms 14, 16, 18, 20 willresult in the hand closing in a natural fashion around a gripped objectof any shape. The first finger or thumb to meet the object (with alldigits) will cease moving and the hydraulic interconnection means thatfluid will continue, without an increase in hydraulic pressure, to movethe digits of the other finger(s) and/or the thumb until all digits ofall the finger and thumb mechanisms are meeting similar resistance, atwhich point the hydraulic pressure will increase and the strength ofgrip of the whole hand increases.

As mentioned above, movement of the fingers is controlled via one or twoEMG sensors controlling a variable speed motor that drives the hydraulicpumps of the system. The hydraulic circuit and its interaction with thevariable speed motor are explained in more detail below. In relation tothe grip from each finger, what is important is that the user can choosewhen to close the hand and when to open the hand, and the digits in eachfinger will grip adaptively as explained above. Therefore, the user isable to stop movement in order to acquire the desired grip, and the usercan also place the hand against an object or use their other hand inorder to resist movement of the fingers/thumb and therefore close thehand with the fingers and thumb in a required pattern. Unlike many ofthe prior art systems there is no requirement for a complicated codesystem requiring a sequence of “clicks” of an EMG sensor in order toplace the hand into a required grip pattern. Instead, it will adaptivelygrip to any object that is presented to it, and also by means ofselectively resisting motion of digits as required the user can placethe hand into any pattern that they require.

The speed and direction of movement of the fingers and thumb iscontrolled by the speed and direction of the electric motor. Thepressure applied is controlled by two hydraulic pumps as discussedbelow, with a hydraulic circuit that switches automatically between alow pressure high-volume configuration and a high-pressure low-volumeconfiguration. The control of the fingers by the speed and direction ofthe electric motor is different to “normal” hydraulics where theelectric motor runs at a continuous speed in a single direction andmultiple valves are used to control the speed and direction of the flowof hydraulic fluid. Controlling both speed and direction of thehydraulic actuators with the electric motor minimises the number ofvalves required. This makes the hydraulic system much simpler andresults in the hydraulic circuit operating in a considerably differentway to “normal” hydraulics. This type of system is only feasible inhydraulic systems with relatively low pressures and small fluid volumes,which works well for an artificial hand, but would not be applicable inall other fields where hydraulics are used.

Since the fingers and thumb are robustly actuated via hydraulics and arespring return then they can be pushed away from their natural positionwithout risk of damaging the mechanism. In particular, the fingers areable to absorb knocks and other intended or inadvertent impacts bymoving against the hydraulics and the springs without risk of damage tothe mechanism of the hand. This is a significant advantage compared tosome prior art products that use lead screws, worm gears, and so on,which are very fragile and vulnerable to damage when the fingers orthumb are knocked.

To provide the required strength and lightness whilst also achieving thecomplex shapes necessary then 3-D printing is used in manufacturing thedevice. The outer bodies for the upper and lower digits of the fingersand thumb mechanisms 14, 16, 18 are 3-D printed in titanium, as is thestructural end plate 66 of the palm unit 12. The main body for the palmunit 12, which is described in more detail below, is in this example 3-Dprinted in plastics, but could be re-engineered to be printed inaluminium or titanium with adjustments to the design for maximum weightsaving (for example, by including additional voids such as in ahoneycomb type construction). The various cables are made of steel inthis example.

As well as providing advantages resulting from the arrangement of thefinger and thumb mechanisms 14, 16, 18 as described above, theartificial hand of FIG. 1 also has important and advantageous featuresin relation to the arrangement of the palm unit 12 and the internalparts thereof. FIGS. 5 to 9 illustrate additional details of theseparts, which are also described below. FIG. 10 is hydraulic schematicfor the palm unit 12 illustrating the arrangement of the high and lowpressure hydraulic pumps and the simplicity of the hydraulic circuit(especially as compared to prior art systems which are fully hydraulicsuch as the “Fluidhand” design). FIGS. 11 to 26 show various componentsof the system in greater detail.

It will be seen from the FIG. 5 that all the hydraulic elements as wellas an electric motor 68 are fully contained within the palm unit 12, andthey are housed in a palm unit body 70, the details of which can be seenin several of the Figures. The palm unit body 70 is shown without anyother parts in FIG. 25, and without any other parts and with a cutawaysection in FIG. 26. As noted above, the palm unit body 70 is 3-D printedout of plastics. In FIG. 5 the structural end plate 66 of the palm unitis removed so that the various connections can be seen in more detail,and the main body 70 is shown transparent for the same reason.

The electric motor 68 has an axis running lengthways along the palm unit12 (from the wrist end toward the finger end) and this axis is parallelto the axis of a shaft that powers the hydraulic pump assembly 72. Theelectric motor 68 is coupled to the shaft of the hydraulic pump assembly72 via a belt 28 that is located outside of the main body 70 of the palmunit 12 allowing better access for assembly and for maintenance. Theelectric motor 68 and the hydraulic pump assembly 72 are placed on theside of the hand opposite to the thumb. Finger piston couplings 32 andthe thumb piston coupling 40 extend from the end of the palm unit body70 from their respective hydraulic cylinders 36, 38 which extend backinto the palm unit body 17 and are also parallel with the axis of themotor along the length of the palm unit 12. Also visible in FIG. 5 arethe ends of two electromagnet controlled valves 90, and these aredescribed in further detail below with reference to FIG. 10 as well asFIGS. 23 and 24.

Details of the palm unit can be seen in cross-section in FIG. 6 and FIG.7, particular for the hydraulic pump assembly 72 and also, in part,hydraulic connection passages and the thumb hydraulic cylinder 38. Thehydraulic pump assembly 72 includes both a low-pressure, high-volume,hydraulic pump 74 and a high-pressure, low-volume, hydraulic pump 76,which receive power from the same shaft 78, turned by the motor 68. Theinteraction of the two hydraulic pumps 74, 76 with the hydraulic circuitwill be explained below in connection with FIG. 10. The shaft 78 passesthrough the high-pressure hydraulic pump 76 to the low-pressurehydraulic pump 74 and operates both hydraulic pumps 74, 76simultaneously. The hydraulic pumps 74, 76 are functionally separate,but they are formed as a single assembly with a common shaft for ease ofmanufacture and assembly. This also saves weight and space as well asallowing the two hydraulic pumps 74, 76 to be mounted within a singlechamber 80 within the palm unit body 70. Beyond the low pressurehydraulic pump 74, and in the same chamber 80 of the palm unit body 70an equaliser 92 is installed. FIGS. 17 and 18 provide a close-up view ofthe equaliser 92. The equaliser 92 operates via spring and generates apositive oil pressure on the suction side of the low and high pressurehydraulic pumps 74, 76. The equaliser 92 acts to prevent cavitation inthe hydraulic pumps 74, 76. The equaliser also moves to adjust theavailable volume of the chamber 80 to compensate for movement of thecylinder rods for the finger and thumb hydraulic cylinders 36, 38, whichwould otherwise result in changes in the volume of the system.

Referring again to FIGS. 25 and 26 it will be seen that as well as thehydraulic pump and equaliser chamber 80 the palm unit body 70 alsoincludes three hydraulic chambers 36′, 38′ to form the hydrauliccylinders 36, 38 for the thumb and two finger mechanisms, two valveopenings 82 for receiving the electromagnet controlled valves 90, avalve opening 84 for receiving a pressure controlled valve 86 (notvisible in FIG. 5, discussed in more detail below with reference toFIGS. 21 and 22) and a motor chamber 88 for holding the motor 68. Thepartially cutaway view in FIG. 26 shows an example of how the hydrauliccircuit is formed as an integral part of the palm unit body 70. All therequired interconnections between the various hydraulic chambers areformed as passages between chambers in a single unit. The use of 3-Dprinting for the palm unit body 70 enables this complicated shape to beformed without undue expense. Since all significant forces on the palmunit body are axial than a relatively soft plastics material can beused, with relatively thin sections between the various axialcomponents. The pressure of the hydraulic fluid within the cylinderscreates radial forces, but these forces act generally symmetrically andthe circular shapes used are effecting in containing these pressureseven with relatively weak plastic materials. Although these thinsections would otherwise be vulnerable to flexing as there are no radialforces then this is not a particular risk for the system. Thisarrangement also provides the advantage that all of the hydrauliccircuit is contained within a single housing 70 and can therefore easilybe kept fully sealed. The proposed palm unit 12 hence presents minimalrisk of hydraulic leakage with increased robustness compared to priorart designs using hydraulic actuation for artificial hands.

Both of the suction and pressure sides of the two hydraulic pumps 74, 76are within the palm unit and connect to various channels through thepalm unit body 70 that form the hydraulic circuit of FIG. 10. Oil (oranother working fluid) is thus transported from the hydraulic pumps 74,76 to the valves without passing outside of the palm unit body 70. Thesuction and pressure sides of the hydraulic pumps 74, 76 are separatedfrom the outside world and all of the hydraulics using O-ring seals. Asthe hydraulic pumps 74, 76 are isolated from the outside world in thisway then there is no need for any hydraulic seals between the hydraulicpump plates. This is because any leakage will only be internal and canto some extent be disregarded. Avoiding the use of hydraulic pump plateseals save space and enables easier faster and cheaper manufacture ofthe hydraulic pump assembly 72.

The other hydraulic parts can similarly easily be isolated from theoutside world by O-rings or similar seals. This makes the wholehydraulic system very robust and easy to assemble and maintain. Sincethe hydraulic cylinders 36, 38 are also formed as a part of the palmunit body 70 then they do not move or rotate with the moving parts andconsequently they can receive hydraulic fluid from fixed channels withinthe palm unit body 70. Each hydraulic part can be individually removedand replaced for maintenance or repair work. There is also an easilyisolated hydraulic subassembly formed by the palm unit body 70 enclosingthe various hydraulic parts and optionally including the structural endplate 66. An orthopaedic workshop could choose to do maintenancein-house, or they could choose to remove the fingers and wrist connectoralong with the motor and send the hydraulic subassembly back to themanufacturer for maintenance or repairs. The hydraulic subassembly isshown in FIG. 8. As well as the various parts that have already beenintroduced the hydraulic subassembly also includes an emergency releasevalve 94, which can be seen in further detail in FIG. 9 and is shown inisolation in FIG. 15 and FIG. 16.

The emergency valve 94 is a mechanical user controlled valve that can beopened in case of any mechanical, hydraulic or electronic failure inorder to release the hydraulic pressure in the system. The valvebypasses the electrically controlled valves 80 and connects the pressuresides of the thumb and fingers cylinders 36, 38 directly to theequaliser 92. Since there is a spring return then the hand willautomatically move to open configuration when the emergency valve ispushed, but no hydraulic fluid is released from the system. FIGS. 15 and16 show the emergency valve in more detail. Mounting and sealing rings100 are fixed in place within the palm unit body 70 and the main shaftof the valve can be slid relative to these rings 100 in order to releasethe pressure from the system if required by the user.

FIG. 10 shows the hydraulic schematic for the system. The basicconnections will have been apparent from the discussion above. The motor68 powers the high-volume low-pressure hydraulic pump 74 and thelow-volume high-pressure hydraulic pump 76. The hydraulic pumps 74, 76provide hydraulic fluid to the index and middle finger cylinders 36 andthe thumb cylinder 38. The index and middle finger cylinders 36 havepistons 96 and piston connectors 32, which are coupled to the maincables 34 for the finger joints as shown in the preceding Figures. Thethumb cylinder 38 has a piston 98 and piston connector 40, which iscoupled to the main cable 34 for the thumb joint, again as shown in thepreceding Figures. FIGS. 11 through 14 show close-up views incross-section and perspective for the pistons 96, 98 and pistonconnectors 32, 40. It will be noted that the diameter of the thumbpiston 98 (and cylinder 38) is slightly larger than the diameter of theindex and middle finger piston 96 (and cylinders 36). This is in orderto balance the forces between the thumb and two fingers when the tips ofthe fingers and thumb close into a pincer grip. The cylinders are springreturn so that when the hydraulic pressure is released, i.e. when thereis no differential in hydraulic pressure between the two sides of thecylinder across the piston, then the system will return to an at restconfiguration when the hand is open. The equaliser 92 is connected tothe suction side of the hydraulic pumps 74, 76 and has the functionexplained above.

The arrangement of the hydraulic pump assembly 72 is shown in greaterdetail in FIG. 19 and FIG. 20. In this example the high-pressurehydraulic pump 76 is a gear pump using straight gears whereas the lowpressure hydraulic pump 74 is a gear pump using helical gears. Helicalgears dampen the sound from the hydraulic pump, which might otherwise bea problem for the low-pressure hydraulic pump 74. The high-pressurehydraulic pump 76 is assembled first, then the axle of the low-pressurehydraulic pump 74 is connected and the low-pressure hydraulic pump isassembled. The axle of the low-pressure hydraulic pump fits to the axleof the high-pressure hydraulic pump with axial play forming a singleshaft 78 that powers both hydraulic pumps. The axial play is provided inorder to keep the gears on each part of the hydraulic pumps' shaftaxially independent of each other, ensuring that there is no interactionof the high and lower pressure parts of the hydraulic pump assemblyduring use.

All of the hydraulic pump plates are manufactured oversize, for example1 mm in excess of the final size. The hydraulic pump plates are joinedtogether by axial bolts 102 in order to form the hydraulic pump assembly72. The hydraulic pump bolts 102 are tightened whilst the gears andshaft are being turned in order to allow for minimal tolerances betweenthe gears and plates of the hydraulic pump and ensure that there isminimal play between gears and plates to thereby minimise the internalleakage. This allows for very little leakage despite the fact thathydraulic pump seals have been dispensed with as noted above. Onceassembly is complete then the hydraulic pump assembly 72 is machined tothe required final size and fitted with the required O-ring seals. Thisproduction method ensures that the hydraulic pump assembly 72 willalways be the correct size for its chamber 80 in the hand palm andprovides a cheap and quick way to produce the hydraulic pumps whilstguaranteeing high quality seals between the hydraulic pump and theoutside world.

FIGS. 21 and 22 show the pressure controlled valve 86 that is used toswitch between high and low pressure operation as described below.Typically the switching pressure would be set at between 10 to 15 bar,and this can be adjusted by a screw 104. When the preset pressure isreached then the valve switches position and flow of hydraulic fluidfrom the low-pressure hydraulic pump 74 is redirected as explainedbelow.

The other two valves of the system are electromagnet controlled valves90 as shown in FIGS. 23 and 24. They operate as one-way valves and canbe held in the open position via an electromagnet. One electromagnetcontrolled valve 90 is connected between the hydraulic pumps 74, 76 andthe actuation cylinders 36, 38 for the fingers and the thumb and has thefunction of preventing hydraulic fluid from flowing out of the fingerand thumb cylinders 36, 38 when the fingers are in the desired position.This valve hence acts as a finger locking valve 90 and makes sure thatthe motor 68 can be stopped without the risk of movement of the fingersaway from the required position. Using a one-way hydraulic valve in thisway saves battery life and means that there is no noise from the handwhen the required finger position or grip of an object has beenachieved.

The second electromagnet controlled valve 90 acts to close the channelbetween the high and low pressure hydraulic pumps 74, 76 when the systempressure increases over a set threshold and the pressure controlledvalve 86 is opened. This valve 90 hence acts as a pressure retainingvalve 90. Considering FIG. 10, it will be understood that duringlow-pressure operation both hydraulic pumps are connected to thecylinders 36, 38 and thus the high-volume low-pressure hydraulic pump 74dominates leading to a fast movement of the pistons 96, 98 until thereis resistance, for example as the fingers and thumb begin to grip anobject. As described above the interconnection of the hydrauliccylinders and the design of the fingers to provide an adaptive gripmeans that the digits and fingers will move adaptively until there isresistance to motion of each part. When there is resistance to themovement of each part then the pressure in the system will begin toincrease, increasing the grip strength from the hand. As the thresholdvalue is reached then the pressure controlled valve 86 opens and thesecond electromagnet controlled valve 90 will close. At this time thehigh-pressure hydraulic pump 76 takes over and the system pressure canincrease above the threshold, for example up to 50 bar, to furtherincrease the grip strength. This combination of low and high pressureoperation allows for an initial fast movement of the fingers with a lowgrip strength followed by the possibility of increasing the gripstrength of the fingers to a significant degree using the high-pressurehydraulic pump 76. Whilst the pressure controlled valve 86 is opened thelow-pressure hydraulic pump 74 continues to operate and simplyre-circulates hydraulic fluid through the pressure controlled valve 86back to the suction side of the low-pressure hydraulic pump 74.

This recirculation of hydraulic fluid from the low-pressure hydraulicpump 74 can easily be understood with reference again to FIG. 10. If thepressure controlled valve 86 is open and the lower electromagnetcontrolled valve 90 is closed then the low-pressure hydraulic pump 74will recirculate fluid, without any pressure building up, around thelower loop of the system as shown in the Figure. When this is occurringthen the high-pressure hydraulic pump 76 will be supplying low-volumehigh-pressure hydraulic fluid to the cylinders 38, 36 thereby allowingthe increased strength of grip.

Also as seen in FIG. 10 the emergency valve 94 sits between the suctionside of the hydraulic pumps 74, 76 and the cylinders 36, 38, and thusenables discharge of pressure from the cylinders in the event of anyhydraulic or electrical failure, or other system failure.

As noted above, the motor 68 can be driven with varying speed inaccordance with signals from the EMG sensor(s). In order to open thefingers the motor 68 is reversed. Thus, the user can easily control thespeed of movement of the fingers both when opening and when closing thehand. Opening of the fingers will also occur naturally via the springsin the cylinders 36, 38 and the return springs 30, 70 mounted betweenthe fingers and the palm unit 12. Since the fingers are locked in placeby actuation of the electromagnetic valve 90 that forms the fingerlocking valve 90 then it is also necessary to have a smallmicroprocessor routine to unlock the fingers and thereafter keep thefinger locking valve 90 open so that the fingers can be opened (with theopening movement being controlled by the user as explained above). Firstthe high-pressure hydraulic pump is operated forward in order to pushthe finger locking valve 90 open, and this valve can then be kept openby the electromagnet. The hydraulic pumps are stopped and thenpressurised again at a lower pressure in order to allow the secondelectromagnet controlled valve 90, which is acting as a pressureretaining valve when in high-pressure operation, to be opened and againthis is held open by the electromagnet. With both of the electromagnetcontrolled valves 90 being open then the hydraulic pumps can now becontrolled with the motor running in reverse in order to open the hand.The unlocking action can be performed in a fraction of a second and iscontrolled by the microprocessor in response to a signal from the EMGsensor indicating that the user is trying to open the hand. Essentially,this process can be invisible to the user.

What is claimed is:
 1. A palm unit for an artificial hand, the palm unitcomprising: a palm unit body; a motor held by the palm unit body; ahydraulic pump assembly held by the palm unit body and comprising alow-pressure hydraulic pump and a high-pressure hydraulic pump, whereinboth hydraulic pumps are powered simultaneously by the motor; and ahydraulic circuit held by the palm unit body and coupled to bothhydraulic pumps, wherein the hydraulic circuit has a low-pressureconfiguration in which the discharge sides of both hydraulic pumps arecoupled to one or more hydraulic actuator(s) for the artificial hand anda high-pressure configuration in which the discharge side of thelow-pressure pump is isolated from the hydraulic actuator(s) andrecirculates fluid to the suction side of the low pressure pump with thedischarge side of the high-pressure pump remaining coupled to thehydraulic actuator(s), and wherein the hydraulic circuit is arranged toswitch from the low-pressure configuration to the high-pressureconfiguration automatically during a closing grip pattern when thepressure in the system increases beyond a threshold value.
 2. A palmunit as claimed in claim 1, comprising a pressure controlled mechanismfor switching the hydraulic circuit from the low-pressure configurationto the high-pressure configuration.
 3. A palm unit as claimed in claim2, wherein the discharge side of the low-pressure pump is coupled to thedischarge side of the high-pressure pump via a one-way valve permittingflow from the low-pressure pump toward the high-pressure pump and thedischarge side of the low-pressure pump is coupled to the suction sideof the low-pressure pump via the pressure controlled valve.
 4. A palmunit as claimed in claim 3, wherein the one-way valve can be held openfor two-way flow, for example to allow for reverse flow of fluid throughthe circuit during opening of the hand.
 5. A palm unit as claimed inclaim 2, wherein the one-way valve is an electromagnet controlled valve.6. A palm unit as claimed in claim 1, wherein the motor is a variablespeed motor.
 7. A palm unit as claimed in claim 1, wherein the motor isa reversible motor.
 8. A palm unit as claimed in claim 1, comprisingmultiple hydraulic actuators, wherein the hydraulic circuit is arrangedso that the pressure and suction side of each of the hydraulic actuatorsis linked to equalise the pressure in the hydraulic fluid within themultiple actuators.
 9. A palm unit as claimed in claim 1, wherein thereare fewer hydraulic actuators than the number of fingers and thumbs onthe artificial hand.
 10. A palm unit as claimed in claim 9, wherein thepalm unit does not include a separate hydraulic actuator for the littlefinger and optionally also it does not include a separate hydraulicactuator for the ring finger.
 11. A palm unit as claimed in claim 9,wherein fingers without their own hydraulic actuator are resilientlycoupled to an adjacent finger that does have an actuator.
 12. A palmunit as claimed in claim 1, wherein the hydraulic pump assembly is asingle unit including both the high-pressure and the low-pressurehydraulic pump, and this single unit is arranged to fit within a singlechamber in the palm unit.
 13. A palm unit as claimed in claim 1, whereinthe pump assembly is sealed from the outside world within the palm unit.14. A palm unit as claimed in claim 1, wherein the pump assemblyincludes a hydraulic axle seal for a shaft between the two pumps, butdoes not include any seals between pump plates of the pump.
 15. A palmunit as claimed in claim 1, wherein both of the hydraulic pumps areactuated by a single shaft powered by the motor.
 16. A palm unit asclaimed in claim 15, wherein a shaft powered by the motor passes throughone of the pumps in order to reach the other pump.
 17. A palm unit asclaimed in claim 16, wherein the shaft may be split in two, having alow-pressure section and high-pressure section driving the respectivehydraulic pump, with axial play between the two sections.
 18. A palmunit as claimed in claim 1, wherein the pump assembly is assembled froma number of pump plates assembled together and held with bolts extendingthrough the length of the pump assembly.
 19. A palm unit as claimed inclaim 1, wherein the pump assembly is generally cylindrical in form andis arranged to be inserted and sealed within a cylindrical chamber inthe palm unit.
 20. A palm unit as claimed in claim 1, wherein the palmunit body forms a sealed enclosure for all hydraulic parts including thehydraulic circuit and hydraulic pump assembly.
 21. A palm unit asclaimed in claim 1, wherein the palm unit body is formed in a singlepiece.
 22. A palm unit as claimed in claim 21, wherein the palm unitbody is formed by 3-D printing.
 23. A palm unit as claimed in claim 21,wherein all hydraulic connections for the hydraulic circuit are formedby channels within a single piece palm unit body.
 24. An artificial handincluding a palm unit comprising a palm unit body; a motor held by thepalm unit body; a hydraulic pump assembly held by the palm unit body andcomprising a low-pressure hydraulic pump and a high-pressure hydraulicpump, wherein both hydraulic pumps are powered simultaneously by themotor; and a hydraulic circuit held by the palm unit body and coupled toboth hydraulic pumps, wherein the hydraulic circuit has a low-pressureconfiguration in which the discharge sides of both hydraulic pumps arecoupled to one or more hydraulic actuator(s) for the artificial hand anda high-pressure configuration in which the discharge side of thelow-pressure pump is isolated from the hydraulic actuator(s) andrecirculates fluid to the suction side of the low pressure pump with thedischarge side of the high-pressure pump remaining coupled to thehydraulic actuator(s), and wherein the hydraulic circuit is arranged toswitch from the low-pressure configuration to the high-pressureconfiguration automatically during a closing grip pattern when thepressure in the system increases beyond a threshold value along withartificial fingers and a thumb.
 25. An artificial hand as claimed inclaim 24, wherein the fingers and thumb have mechanical joints arrangedto be actuated by hydraulic actuators within the palm unit. 26.(canceled)